Although the specification focuses on the analysis of paper (and more particularly quantifying the quality of the paper by counting and categorizing the dirt particle content), the apparatus of the present invention may be utilized for analyzing other materials. In this regard, any material manufactured in web form such as viscose, cellulose, cardboard, fabric and other similar materials may also be analyzed by the present invention. The present invention may be advantageously utilized to analyze any material property (such as dirt count) which is quantifiable by the measurement of the intensity of light reflected by the material being analyzed.
Paper is typically formed by spraying pulp fibers onto a web and allowing the fibers to dry. Although pulp processing typically involves filtering the pulp to eliminate contaminants, inevitably varying levels of dirt particles contaminate the processed pulp and degrade the quality of the paper being manufactured.
The degree to which the pulp is contaminated by dirt significantly impacts the applications to which a paper product may be utilized. In this regard, only paper with a relatively low dirt particle count would be considered for use in a hardbound, high quality novel. Alternatively, paper utilized to form sandwich bags may have a relatively higher degree of dirt particle content.
Typically, a paper manufacturer utilizes pulp to initially fabricate a square meter test sheet of paper. The test sheet is then cut into individual sheets, e.g., 8 1/2" by 11". These individual sheets are then visually inspected and measured for dirt in accordance with conventional TAPPI T-437 specifications.
A dirt count measurement is then obtained based on a visual comparison of dirt spots shown in the TAPPI specifications with the dirt particle configuration shown on the individual sheets of the square meter sample. In this manner, the inspector selects a size category from the TAPPI specifications which most closely matches the size of the dirt particles found on the sample sheets.
After analyzing each of the individual sheets of the square meter sample, the inspector adds the data obtained from the TAPPI specifications to quantitatively assess how many millimeters of dirt are present on each sheet to ultimately determine the number of square millimeters of dirt in the square meter sample. Thereafter, values are computed which hopefully reflect the dirt present in the square meter sample in parts per million. The parts per million dirt particle value is then utilized by the paper manufacturer to determine whether the pulp is of an acceptable quality.
Because the readings obtained by visual inspection are highly subjective, such readings are inherently inaccurate. Accordingly, the ultimate value obtained for a given test sheet is highly dependent on the individual inspector. Such a value can be expected to vary significantly if a different inspector were to evaluate the same test sheet.
Attempts have been made to automate dirt particle counting and categorizing in the paper industry. One currently available dirt particle counting system was originally designed for counting bacteria cultures.
In currently available particle counting systems, postage stamp size regions of a paper product are sampled and the dirt particle content analyzed for these small regions. Thereafter, such systems project the overall paper quality based on the samples taken. Such systems fail to generate an accurate representation of the dirt particle content of an entire square meter of a paper test sheet since the dirt particles tend to be randomly distributed thereby precluding obtaining a representative sample of small regions. If a large number of dirt particles are distributed in a non-sampled portion of such a test sheet, the particle count projection will not be accurate.
The present invention recognizes that the field of view of such systems may not be adequate to accurately quantitatively analyze the dirt particle content of paper sample on the order of the conventionally inspected one square meter sample size.
The present invention utilizes a microcomputer based digital analysis system which includes a microcomputer and a flatbed optical scanner to analyze test sheets of paper fabricated from a batch of pulp to be tested. A keyboard is utilized by an operator to select one of a predetermined number of reports. After a report is selected, a menu is displayed on a CRT which enables the operator to start the sample tests under the control of the microcomputer.
Once the total document is scanned either by operator manipulation or under the control of an automatic document feeder, the microcomputer tabulates the data retrieved during each of the individual sheet tests as necessary to generate the report selected by the operator.
The microcomputer processes the image data on a line by line basis. A dot buffer is created having a location for each pixel across the scanned line, wherein numbers are incremented as dots having image data are encountered in the scanned line. A dirt array is also created which contains the sum total of tabulated areas from the dot buffer in pixels for each contiguously connected group of pixels that have values greater than a recognition threshold. The dirt array is a summation array for each speck of dirt detected which stores data representative of the size of the dirt speck.